In early nineties of the 20th century, an optical-angle-based color-changing anti-counterfeiting product appeared in foreign countries, i.e. notable color change occurs to patterns along with the change of viewing angle. This type of product has characteristics of being a leading technology, being liable to be distinguished, a high security and being convenient for identification. Thereby, said technology has become one of the widely used technologies by authoritative organizations of public security of countries in global. Currently, this technology has been successfully applied to many fields such as countries' currency and certificate (e.g. rmb, dollar, euro, foreign passport, driving license). However, regarding the traditional optical-angle-based color-changing anti-counterfeiting product, for example, optically variable ink OVI, optically variable hologram film and the like, the optically variable effect of the material thereof is achieved by the technology of pigment interference, optical coating or laser etching. Thereby, the product has the defects of non-perspective, a long technique route, a difficulty in combination of different technologies, and a high price, which have greatly limited the application scopes of the traditional anti-counterfeiting product.
A novel optical-angle-based color-changing material can selectively reflect lights having a special wavelength via a helical structure in the material, thus macroscopically exhibits an effect of optical-angle-based color change, and, this type of material is a transparent material. At present, this type of optical-angle-based color-changing material includes optical-angle-based color-changing chiral polymer material (e.g. CN03114913.8), optical-angle-based color-changing cellulose material (e.g. CN02136974.7) and so on.
The technology of directional retroreflection belongs to a physical optical technology and was earlier developed by Chinese American scientist Dr. DONG Qifang in fifties of 20th century. The major technical principle is: when a parallel light beam irradiates a surface having special structure from a certain angle, a comparatively large part of light reflects in parallel light beam towards incident direction of light source. The ray passes through incidence-refraction-reflection course and forms a directional retroreflective characteristic, generating particular reflection effect. With the development of automobile industry and road traffic, a series of reflective materials based on this technical principle are widely used, and, more and more technologies relating to structure design and manufacturing method of the reflective materials are patented, for example, the U.S. Pat. No. 4,721,649.
However, the above anti-counterfeiting technologies about optical-angle-based color change have similar effects, and lack technical concealment; application of the technology of directional retroreflection is currently limited to road traffic and the like field. Thus, the present invention studies a combination of the technology of directional retroreflection with the technology of optical-angle-based color change, and develops novel anti-counterfeiting film that has special visual effect to meet requirements of advanced anti-counterfeiting field.